An initial discussion on major controlling factors on formation of coal-formed large-medium gas fields

The so-called "large-medium gas field" means a gas field with proven reserv es equal to or larger than 100x10(8) m(3). Up to 1997, 23 coal-formed great -medium fields are discovered in China, excluding two in Taiwan Province. T heir proven reserves take 50.9% in total natural gas reserves. Therefore, t he coal-formed great-medium gas field plays a decisive role in natural gas reserves and the study of their controlling factors is very important both in theory and in practice. There are six major controlling factors on the f ormation of coal-formed large-medium gas fields: ( i) The generating center of coal-formed gas and its surrounding area; (ii) low potential area; (iii ) late pool-forming period; (iv) traps related to the paleo-uplifits in coa l-formed gas area; (v) above or between abnormally pressured compartments; (vi) faulted traps related to coal-bed.